| |
 |
UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 1:24 |
 |
|
|
|
Conference: Bucharest University Faculty of Physics 2005 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
Magnetic properties of a loess-paleosol sequence at Mostiştea (Romania)
Authors:
C. Necula, C. Panaiotu, C.E. Panaiotu, A. Grama
Affiliation:
University of Bucharest, Paleomagnetic Laboratory
E-mail
c3necula@yahoo.com
Keywords:
loess-paleosol, hysterezis parameters, Day plot, Curie temperatures, rock-magnetic parameters, grain size.
Abstract:
We report here the analysis of the magnetic properties of a loess-paleosol sequence from South-Eastern Romania. Thermomagnetic curves, various hysteresis parameters, magnetic susceptibility, isothermal, anhysteretic and viscous remanence were measured for representative samples for loess and paleosol layers. The variation of magnetic susceptibility with temperature in chernozemic soils and paleosols shows a sharp decrease at 300°C followed by an increase just below the Curie temperature of magnetite (580°C). This behavior is characteristic for maghemite which inverts during heating to a phase assemblage that include magnetite. The brown forest paleosol had a Curie point around 580°C indicating magnetite as main magnetic phase. Loess samples are also dominated by magnetite, but small amount of hematite is probably also present. These results are in agreement with the isothermal remanence acquisition and demagnetization curves. Grain size trend of magnetite in loess and paleosol was established using the rockmagnetic data presented by Peters and Dekkers (2003). All the data show that loess is dominated by single domain (SD) to multidomain (MD) magnetite (but probably less than 1 μm). Our results demonstrate that most of magnetite grains in paleosol are at the limit superparamagnetic (SP) – SD (below 0.1 μm). Hysteresis parameters, according to Dunlop (2002), indicate that both paleosol and loess data cluster in the pseudo-single-domain (PSD) region. Indication about an important quantity of superparamagnetic magnetic grains in paleosols comes mainly from viscous decay of isothermal remanence and from frequency dependent susceptibility. All rock magnetic measurements show that pedogenetic processes has changed the main population of magnetite grains from relative coarse crystals in loess, in the range SD-MD, to a dominant population with fine crystals in the SP-SD range in paleosols.
|
|
|
|